1. Field of the Invention
The present invention relates to driving mechanisms using belts for transmitting power.
2. Description of the Related Art
Driving systems using belts such as toothed belts, or belts, are frequently used in office machines and industrial robots. FIG. 9 shows such a conventional belt-drive mechanism. In FIG. 9, a slider 2 is secured to a toothed belt 1. The toothed belt 1 is disposed between a driving pulley 3 and a driven pulley 4. When the driving pulley 3 rotates, the belt 1 moves the slider 2 in the direction indicated by arrow X. The distance between the centers of the driving pulley 3 and the driven pulley 4 is called a stroke ST.
This slider driving system using a toothed belt has advantages such as low cost, few limitations against speed, and easy provision of a long stroke. Since the toothed belt is less rigid than a ball screw, however, precision in movement distances decreases due to friction or the stick-slip motion of a guide (not shown) and vibration tends to occur. The main reason for these drawbacks of the toothed belt is low rigidity of the belts. The rigidity of the belts decreases by half when the stroke is doubled, substantially restricting its applications.
FIG. 10 shows a ball screw, another conventional drive system. The spline 5 of the ball screw engages with the nut 7 of a slider 6. When a motor 8 drives the spline 5 such that the spline 5 rotates in the direction indicated by arrow R, the slider 6 moves in the direction of arrow X. A long ball screw is expensive. In addition, ball screws having various lengths have to be prepared to meet the required stroke. The maximum speed of a ball screw is restricted by the lead length and the critical revolution frequency.